1. Field of the Invention
This invention relates to the field of probe positioning methods and systems, and particularly to methods and systems used to locate test probes on micro-sized devices.
2. Description of the Related Art
The testing of "micro-sized" devices, i.e., integrated circuits (ICs) and micro-electromechanical (MEM) devices, prior to their assembly into closed packages, requires the use of one or more very small test probes. For an IC, the test probes are used to sense or apply electronic parameters, while a MEM device may require the testing of parameters that are, for example, mechanical, fluidic, pneumatic, or acoustic in nature.
Many test probe systems have been developed, primarily for use with ICs. One such system, typical of those in the field, is described in U.S. Pat. No. 5,539,676 to Yamaguchi, which is directed to a system for probing semiconductor wafers. A probe card holds a fixed array of probes, and the wafer is mounted on a movable table. The positions of the probes are known relative to a point on the card, and this information is stored in a memory device. A camera is moved so that a reference probe is aligned with a reference point in the view field of the camera. A processor uses the camera position information to determine the absolute coordinates of the reference probe, from which the positions of each of the other probes can be calculated. All of the test probes on the probe card are simultaneously brought into contact with the wafer to be tested. There is no means by which an individual feature on the wafer can be targeted for probing, nor of uniquely identifying an individual probe from among the probe card's array of probes.
Another Yamaguchi patent (U.S. Pat. No. 5,530,374) discloses a similar system, except that the camera is aligned with a reference marker on the probe card rather than a reference probe, with the positions of the probes known with respect to the marker. However, the limitations found in the previous system are present here as well.
The Yamaguchi systems work well when a number of identical wafers are to be tested in succession, and the array of points to be probed does not vary from wafer to wafer. However, these systems are not well-suited for use with small numbers of highly unique devices, such as MEM devices. Here, different probe types may be needed to accommodate the different parameter types that might be found on a MEM device. Furthermore, due to the interdisciplinary nature of a MEM device, which may combine mechanical, electric, and fluidic aspects, for example, it is likely to have a much more irregular surface than that of an typical IC wafer. Conventional high volume probe card-based test probe systems are unable to provide the kind of flexibility called for in this type of application.